Plate-shaped pressed bodies

ABSTRACT

There is disclosed a plate-shaped pressed body (wafer) produced from an inorganic sorbent and a binder, having a thickness of less than 700 μm, which is produced by the process of compressing a mixture of the inorganic sorbent, the binder, and optionally water and compression aids at a pressure of at least 70 MPa, wherein the weight ratio of dry sorbent to dry binder is between about 4 and 0.7 and the water content of the mixture, measured at 160° C., is between 8 and 20%; and calcining the resulting pressed body at temperatures of at least about 500° C., until the water content is substantially removed.

FIELD OF INVENTION

[0001] The invention relates to plate-shaped pressed bodies (wafers)prepared from an inorganic sorbent and a binder, having a thickness ofless than 700 μm, which are characterized by a high mechanical strengthand a low brittleness and which are capable of effectively absorbinginorganic and organic gases or vapors.

BACKGROUND OF INVENTION

[0002] The manufacture of pressed bodies, in particular of tablets, onthe basis of zeolites and binders is known. Thus, according to JP-A-6115 5216, zeolite tablets are prepared by mixing a zeolite, a binder anda lubricant, and extruding the mixture. These are tablets with the samedimensions in all directions.

[0003] From JP-A- 56 06 3818 the manufacture of zeolite tablets for useas gas adsorbents is known. Powdered and dried (at 105 to 110° C.)zeolite is mixed with 8.1% by weight of bentonite powder and the mixtureis kneaded with a 4% aqueous urea solution. The mixture is thentabletted, dried and calcined at 510° C. The increase of the compressivestrength of the tablet is caused by the urea content.

[0004] From JP-A-55 16 5144 it is known to knead zeolite powder forcooling aggregates in powder form with bentonite and water. The mixtureis extruded to form round particles with a diameter of 0.8 to 10 μm.

[0005] According to JP-A-55 10 4913, zeolite in the Na-form is mixedwith 25% by weight clay, kneaded with water, extruded, calcined at 650°C., immersed in a calcium chloride solution, washed, dried at 110° C.and activated at 400° C. The tablets are used as 11) drying agents.

[0006] According to JP-A-46 03 2572, zeolite powder is mixed with kaolinand Na− (or NH4−)-hydroxyethyl cellulose, shaped, dried and calcined at650° C., in order to increase the strength of the zeolite tablets.

[0007] According to JP-A-21 44 121, deodorants are obtained by extrudingzeolite powder or granules with calcium chloride or bentonite and water.The mixture is then tabletted and calcined.

[0008] According to JP-A-63 21 8234, drying agents are prepared byextruding a mixture of microporous particles (e.g. gypsum, cement,ceramic powder) and an inorganic or organic filler, such as CaCl2, LiCl,Bentonite, zeolites, PVA or other water-soluble polymers. The mixture istabletted and subsequently hardened.

[0009] According to JP-A-60 132 643, zeolite tablets are prepared asdrying agents using 20% sepiolite as a binder. The mixture is kneadedwith water, tabletted, dried at 150° C. and calcined at 550° C. Thetablets have an improved drying efficiency as compared to bentonitetablets.

[0010] The prior art tablets are unsuitable for utilization in a narrowspace and under mechanical-stresses, because they are too thick and tooheavy and have too low a sorption capacity for noxious gases and vapors(based on mass and surface). With the methods and mixtures according tothe prior art, brittle pressed bodies were obtained which crumble, inparticular after calcining.

[0011] It is known that electroluminescent devices function over a longperiod of time only if a drying agent is present. Such drying agents arerequired because of the sensitivity of the electrodes, in particular thecathodes, to moisture (cathodes generally consist of Ca or Mg alloys).Therefore in use, these devices are sealed as efficiently as possibleunder a protective gas.

[0012] The use of a moisture absorber in an electroluminescent device isdisclosed in EP 500 382 A2. The moisture absorber is in the form of apowder or small spheres applied to a black silicone resin coating.According to the preferred embodiment, the drying agent is contained ina gas-permeable bag.

[0013] Likewise, US-A-5,882,761 discloses the use of a drying agent inan electroluminescent device. The preferred drying agent is BaO. Seealso U.S. Patent No. 5,591,379 which discloses a it coating for use withmicroelectronic devices comprising a desiccant powder blended with abinder.

[0014] The sorbents known from the above-mentioned documents have thedisadvantage that they can only absorb water vapor. The cathodes,however, can be degraded by other gases as well, which gases can beformed when the epoxy resin used for sealing is cured (ammonia, liquidamines). In addition, the presence of oxygen may result in a failure ofthe luminescent elements (oxidation of the cathode)

[0015] The present invention is bas ed on the need to provideplate-shaped pressed bodies (wafers) comprising or formed from aninorganic sorbent and an inorganic binder which are very thin (less than700 μm). In spite of being thin, these bodies have high strength and maybe incorporated in particular into electronic elements which only havelimited space available. These bodies are also shock resistant for usessuch as electronic displays in automobiles and mobile telephones.

[0016] The present invention satisfies this need by providingplate-shaped pressed bodies (wafers) comprising or formed from aninorganic sorbent and a binder, having a thickness of less than 700 μm,which are obtainable by a process comprising the steps of compressing amixture comprised of at least one inorganic sorbent, at least one binderand optionally water and a compression aid, at a pressure of at least 70MPa; wherein the mixture has a weight ratio of dry sorbent to dry binderbetween about 4 and 0.7 and a water content of the mixture, measured at160° C., between about 8 and 20%; and calcining the resulting pressedbodies at temperatures of at least 500° C., until the water content issubstantially removed.

BRIEF DESCRIPTION OF DRAWINGS

[0017]FIG. 1 is a side view of an electroluminescent product containinga plate shaped body of Example 4 as discussed in Example 13.

DETAILED DESCRIPTION

[0018] The pressed bodies (wafers) according to the invention have ahigh strength, a low brittleness, a high sorption rate and high sorptioncapacities with a low mass. They exhibit low thermal expansion, are notabraded and may be easily colored by the addition of pigments duringmanufacture.

[0019] The pressed bodies according to the invention may be produced inautomatic processes in large numbers per unit time. They may be easilyhanded and may, for instance, be removed from a storage container by socalled “pick-and-place” machines, and then inserted in an electronicdevice.

[0020] The pressed bodies according to the invention are capable ofabsorbing gases (ammonia, amines, oxygen) in addition to water vapor.Since they have a high sorption capacity, the electronic device intowhich they are to be inserted does not have to be completely sealedair-tight, i.e. the diffusion rate for water vapor into the device canbe greater than zero. Moreover, the choice of a suitable material forsealing the device (e.g. an epoxy resin), is facilitated, as thecritical time in which the said material used must have reached itsfinal and lowest permeability for water vapor can be prolonged by theuse of the wafer.

[0021] Preferably, the inorganic sorbent is a natural or syntheticzeolite. However, other sorbents, such as amorphous silica or aluminumhydroxide, or mixtures of two or more sorbents, may also be used.

[0022] In general, any binder which is known to a person skilled in theart may be used as the binder. Preferably, a smectite clay, especiallybentonite, is used as the binder. Moreover, the use of other inorganicbinders, such as aluminum oxide-hydroxide (pseudo-Boehmite), ispermissible. Organic binders based on carbohydrates or proteins may alsobe used, for instance starch, cellulose derivatives (such as CMC orCEC), casein, as well as synthetic polymers, such as PVA, PVP orpolyphenols or tannin-containing binders (quebracho). Also, mixtures ofdifferent binders may be used.

[0023] By the addition of the bentonite to the zeolite, the sorptioncapacity of the latter is surprisingly not reduced. In fact, asynergistic effect can be observed, i.e. the sorption of water vapor bythe mixture is far less reduced than would be expected by merecalculation based on the percentages of the bentonite added to thecomposition.

[0024] The thickness of the wafers is preferably about 200 to 400 μm,its binder content is preferably about 40 to 50% by weight.

[0025] The invention also relates to a process for preparing the pressedbodies as defined above, which process is characterized in that amixture comprised of or containing at least one inorganic sorbent, atleast one binder and optionally water and compressing aids is compressedat a pressure of at least about 70 MPa, wherein in the mixture theweight ratio of dry sorbent to dry binder is between about 4 and 0.7 andthe water content of the mixture, measured at 160° C., is between about8 and 20%;

[0026] and calcining the resulting pressed bodies at temperatures of atleast about 500° C. until the water content is substantially removed.

[0027] It has been found that by this process results in particularlyadvantageous pressed bodies with excellent physical and chemicalproperties. Especially advantageous pressed bodies are obtained at amixing ratio of dry sorbent to binder in the initial mixture betweenabout 1.5 and 1.

[0028] The desired water content of the mixture may be adjusted via thewater content of the components (sorbent, binder) and/or by addition ofwater.

[0029] The A-zeolite preferably used as a sorbent is available in powderform and has a moisture content of about 10 to 22%. The bentonitepreferably used as a binder is available in powder form with a watercontent of about 10 to 20. The bentonite 25 used has a montmorillonitecontent of preferably more than 80%, based on its dry weight. Thepreferred compression aids are fatty-acid salts of a divalent ortrivalent metal, such as calcium, magnesium or aluminum stearate.

[0030] It has been found that the best results may be obtained duringcompression of the mixture to pressed bodies if the mixture does notcomprise larger amounts, i.e. not more than about 15%, preferably notmore than about 8%, in particular 0% of particles>250 μm, preferably>200μm, and in particular>150 μm, and if the majority of the particles, i.e.at least 50%, preferably at least 60%, is larger than about 45 μm.

[0031] According to a preferred process, the zeolite and bentonitepowders are mixed in the desired ratio with a sufficient amount of waterto allow granulation of the mixture. Preferably, an intensive mixer isused herein. The amount of water which is added depends on the mixingratio of zeolite and bentonite as well as the colloid chemicalproperties of the bentonite used and may be easily determined by anartisan. After granulation, the mixture is adjusted or dried,respectively, to a water content of about 8 to 20%, the water contentbeing determined at 160° C. Subsequently, the mixture is comminuted toparticle sizes <250 μm, preferably <200 μm, in particular <150 μm asindicated above.

[0032] It has been surprisingly found that when compressing the mixtureto obtain pressed bodies, the best results may be obtained if themajority of the particles of the mixture have a more or less sphericalform as may be obtained e.g. by spray drying. Therefore, according to aparticularly preferred embodiment, zeolite and bentonite powder areslurried in water using a high-shear stirring device, such as a UltraTurrax stirrer in order to obtain a pumpable slurry which is thenspray-dried by conventional methods. The water content of the mixturemay be adjusted to the preferred range between about 8 And 20% (thewater content is determined at 160° C.) by controlling the spray-dryingprocess. The adjustment of the particle size distribution so that themixture, as defined above, does not contain large amounts ofparticles>250 μm, preferably>200 μm, and in particular>150 μm, and thatthe majority of the particles is larger than about 45 μm, may also beachieved by appropriate control of the spray-drying process andoptionally subsequent deagglomeration, screening and sorting steps asknown in the art.

[0033] The forming of the pressed bodies from the mixture is performedat a pressure of at least about 70 MPa. The preferred pressure isbetween 100 and 1300 MPa. The compression of the mixture can beperformed in commercially available automatic presses, the constructionof which is known to the artisan.

[0034] In order to allow an efficient production of the pressed bodies,it is important that the formed bodies separate easily and withoutresidual matter from the compression tools. This can be achieved byappropriate choice of surface-modified tools (e.g. steel modified withTiN— or WC), and by ensuring precise control and adjustment of the watercontent of the mixture and control of temperature and humidity at thesite of compression. At low water contents, it is advantageous toprovide a relatively high humidity, e.g. 60 to 80% relative humidity atit about 25 to 35° C. At high water contents, a relatively low absolutehumidity is preferred, e.g. 30 to 50% relative humidity at about 20 to30° C. According to another preferred embodiment anti-sticking agents,such as magnesium or calcium stearate, are applied to the pressure toolsafter a predetermined number of compression cycles, e.g. after each oreach second cycle. Thus, the sticking of the pressed bodies to thecompression tools can be effectively avoided.

[0035] The pressed bodies are calcined at about 500 to 900° C.,preferably at about 650° C., until a constant weight is obtained and thewater content is substantially removed.

[0036] Furthermore, it has been surprisingly found that the arching andbulging of the pressed bodies during calcination may be practicallyeliminated by the application of pressure to the pressed bodies duringthe calcination step.

[0037] According to a preferred embodiment, the application of pressureto the pressed bodies during calcination is provided by the use of aspecially designed belt calcination device wherein the application ofpressure to the pressed bodies is achieved via belts. In general, theapplication of pressure to the pressed bodies during calcination can beachieved by any method, as long as the pressure applied effectivelysuppresses the bulging (curving) of the pressed bodies duringcalcination and does not damage the pressed bodies. In general, apressure between 10 and 30 000 Pa, in particular between 100 and 5.000Pa, may be applied.

[0038] According to a further preferred embodiment, a certain quantityof pressed bodies is stacked in tubes, e.g. tubes made of stainlesssteel or ceramics. Preferably, the tubes are provided with openings(drilling holes) allowing for the evaporation of water duringcalcination. This ensures a rapid and uniform drying. The whole stackwithin a tube is subjected to a pressure sufficient to suppress bulgingof the pressed bodies during calcination without causing fracture,sticking or sintering of the pressed bodies during this process step. Ingeneral, the pressure lies between about 10 and 30.000 Pa, preferablybetween 100 and 5,000 Pa. The wafers calcined under application ofpressure according to the invention, are flat and show no or only aminimal curvature or bulging, which is a prerequisite for use inelectroluminescent devices.

[0039] According to a further preferred embodiment the calcinationtemperature is increased stepwise in order to prevent the formation offractures and cracks in the pressed bodies due to fast, non-uniformevaporation of water.

[0040] The pressed bodies may also be calcined under vacuum and cooled,whereby they are capable of sorbing permanent gases, such as oxygen.

[0041] Furthermore, the pressed bodies may contain coloring pigments,such as Fe₃O₄.

[0042] The invention further relates to the use of the above-definedpressed bodies as inserts in electronic devices or elements, such asdisplays, in particular electroluminescent elements, such as organiclight-emitting diodes (LED). However, they may also be used inmoisture-sensitive liquid crystal displays (LCD).

[0043] These devices or elements may be damaged by inorganic or organicgases or vapors during manufacture or during use. However, in view oftheir construction, they have only limited space available for asorption agent.

[0044] These electronic devices or elements (e.g. displays in motorvehicles and mobile telephones) are frequently exposed to strong shocks.It is therefore important that the pressed bodies not break or crumble.In view of their strength, it is not necessary to cover the pressedbodies with a gas-permeable foil, which simplifies the manufacture ofthe electronic elements.

[0045] As compared to BaO, a significant volume and cost reduction ofthe electronic element may be achieved. Thus, the wafers (related totheir mass) have a higher sorption capacity and sorption rate for watervapor within the required temperature and moisture range in anelectronic element. In addition, when using Bao, it should be noted thatan increase of the volume of the material by 100% occurs during thehydration reaction. Therefore, an additional volume for the expansion ofthe drying agent must be provided within the element, and a water-vaporpermeable foil must be applied between the BaO and theelectroluminescent layer to avoid contact between the expanding andpossibly crumbling drying agent and the layer. In contrast, the wafers(according to the invention) do not show a change of volume whenabsorbing water, and remain mechanically stable. Therefore, the presenceof an additional expansion volume with the element and the applicationof a protective foil are not necessary.

[0046] Bao has the additional disadvantage that it or its hydrationproducts exhibit a strong basic reaction. Furthermore, there is a stronglocal heating when absorbing moisture. In direct contact with organiccompounds it also has a tendency toward self-ignition. This limits theselection of polymers for the above-mentioned protecting foils to veryexpensive polymers, e.g. fluoropolymers, and thus increases the costs ofthe element. In addition, when using Bao, disposal problems arisebecause, being a hazardous chemical, the dismantling, re-use anddisposal of the individual parts of the electronic elements are rendereddifficult.

[0047] The pressed bodies according to the invention can also be usedfor other purposes, e.g. as inserts for pharmaceutical packages, becauseof the limited volume which is available within the package for theaccommodation of a drying agent.

[0048] The pressed bodies may be present in any form, for instance theymay be round, square, triangular or rectangular, and may include holesand/or voids. The pressed bodies according to the invention aredust-free and abrasion-resistant. They may be manufactured in commonpress automats in a very large number per unit time.

[0049] The invention is illustrated by the following examples:

EXAMPLE 1 (Comparison)

[0050] 75.2 kg zeolite 4A (water content 20%), 23.8 kg bentonite (watercontent 12%) and I kg calcium stearate were mixed in an intensive mixerfor 2 minutes. Water was added until there was a substantial increase inviscosity, and mixing was continued for 4 minutes. The mixture was driedto a water content of 12% at 110° C., and subsequently granulated(Stokes granulator) and sieved (250 μm). 0.22 g of the material with aparticle size of <250 μm were pressed to a round wafer under a pressureof 69 MPa. The wafers were calcined at 650° C. for 3 hours, cooled withthe exclusion of moisture and packed air-tight. The thickness of thewafers increased by about 15 to 25% upon calcination.

[0051] Product Properties: Thickness: 300 ± 50 μm Moisture content <1%(after calcination): Production rejects: >90% Dropping test*: 100%fracture, wafer crumbles at the periphery

EXAMPLE 2 (Comparison)

[0052] 57 kg zeolite 4A (water content 20%), 42 kg bentonite (watercontent 12%) and 1 kg calcium stearate were mixed in an intensive mixerfor 2 minutes. Water was added until there was a substantial increase ofviscosity, and mixing was continued for 4 minutes. The mixture was driedto a water content of 12% at 110° C., and subsequently granulated(Stokes granulator) and sieved (250 μm). 0.22 g of the material with aparticle size of <250 μm were pressed to a wafer under a pressure of 69MPa. The wafers were calcined at 650° C. for 3 hours, cooled with theexclusion of moisture and packed air-tight.

[0053] Product Properties: Thickness: 300 ± 50 μm Moisture content <1%(after calcination): Production rejects: 75% Dropping test: 80% fracture

EXAMPLE 3

[0054]57 kg zeolite 4A (water content 20%), 42 kg bentonite (watercontent 12%) and 1 kg calcium stearate were mixed in an intensive mixerfor 2 minutes. Water was added until there is a strong increase ofviscosity, and mixing was continued for 4 minutes. The mixture was driedto a water content of 12% at 110° C., and subsequently granulated(Stokes granulator) and sieved (250 μm). 0.22 g of the material with aparticle size of <250 μm were pressed to a wafer under a pressure of 72MPa. The wafers were treated as in Example 2.

[0055] Product Properties: Thickness: 300 ± 50 μm Moisture content <1%(after calcination): Production rejects: <50% Dropping test: 609%fracture

EXAMPLE 4

[0056]57 kg zeolite 4A (water content 20%), 42 kg bentonite,(watercontent 12%) and 1 kg calcium stearate were mixed in an intensive mixerfor 2 minutes. Water was added until there is a substantial increase ofviscosity, and mixing was continued for 4 minutes. The mixture was driedto a water content of 12% at 110° C., and subsequently granulated(Stokes granulator) and sieved (250 μm). 0.22 g of the material with aparticle size of <250 μm were pressed to a wafer under a pressure of 350MPa. The wafers were calcined at 650° C. for 3 hours, cooled with theexclusion of moisture and packed air-tight.

[0057] Product Properties: Thickness: 300 ± 50 μm Moisture content <1%(after calcination): Production rejects: <25% Dropping test: 15%fracture Sorption capacity* after 1 hour 5.4% by weight after 5 hours7.2% by weight after 24 hours 13.0% by weight

[0058] Example 5

[0059] The procedure of Example 4 was repeated except that thecalcination of the wafers was carried out in vacuum. The calcined wafershad essentially the same product properties as the wafers of Example 4,but they additionally showed a sorption capacity for oxygen of about 5ml/g (determined in a dry oxygen atmosphere).

EXAMPLE 6

[0060] 56.5 kg zeolite 4A (water content 20%), 41.5 kg bentonite (watercontent 12%), 1 kg calcium stearate and 1 kg quebracho were mixed in anintensive mixer for 2 minutes. Water was added until there was asubstantial increase of viscosity, and mixing was continued for 4minutes. The mixture was dried to a water content of 12% at 110° C., andsubsequently granulated (Stokes granulator) and sieved (250 μm). 0.22 gof the material with a particle size of <250 μm were pressed to a waferunder a pressure of 200 MPa. The wafers were calcined at 650° C. for 3hours, cooled with the exclusion of moisture and packed air-tight.

[0061] Product Properties: Thickness: 300 ± 50 μm Moisture content <1%(after calcination): Production rejects: <35% Dropping test: 10%fracture

EXAMPLE 7

[0062] The procedure of Example 4 was repeated except that thecompression pressure was 1200 MPa. The dropping test yielded 10%fractures. The rejects were <10%.

EXAMPLE 8

[0063] The procedure of Example 4 was repeated except that 54 kg zeolite4A, 40 kg bentonite, 5 kg Fe3O4 and 1 kg calcium stearate are used. Theresulting wafers were dark in color and could be used for a contrastsurface in a LED display.

EXAMPLE 9

[0064] 110.5 kg zeolite 4A (water content 20%), 76.0 kg bentonite (watercontent 12%) and 1.9 kg calcium stearate were slurried in a high-shearstirring device in sufficient water to obtain a pumpable slurry. Theslurry (suspension) was spray-dried so that a powder with a watercontent of 9.2% (determined by drying at 160° C.) and a particle sizedistribution of 0%>150 μm and 30%<45 μm was obtained. 0.17 g of thismaterial are compressed to a wafer having a diameter of 20 mm using apressure of 190 MPa, the partial pressure of water vapor in theenvironment (air) surrounding the compression tools set to about 30mbar. The wafers were calcined under the application of pressure for 3hours at 650° C. 300 wafers were stacked in stainless steel tubes withdrilling holes (openings) (height 120 mm, inner diameter 20 mm), and thestack was subjected to a pressure of 2.550 Pa. Following calcination,the wafers were cooled under exclusion of moisture and packed.

[0065] Product Properties: Thickness: 300 ± 50 μm vertical dimension:<350 μm (thickness + curvature (bulging)) Moisture content <1% (aftercalcination): Production rejects: <5% Dropping test: <1%

EXAMPLE 10

[0066] 110.5 kg zeolite 4A (water content 20%), 76.0 kg bentonite (watercontent 12%) and 1.9 kg calcium stearate were slurried in a high-shearstirring device (Ultra-Turrax stirrer) in sufficient water to obtain apumpable slurry. The slurry (suspension) was spray-dried so that apowder with a water content of 12.6% (determined by drying at 160° C.)and a particle size distribution of 0%>150 μm and 260%<45 μm wasobtained. 0.17 g of this material was compressed to a wafer having adiameter of 20 mm using a pressure of 210 MPa, the partial pressure ofwater vapor in the environment (air) surrounding the compression toolswas about 17 mbar. The wafers were calcined under the application ofpressure for 3 hours at 650° C. Thus, 300 wafers were stacked instainless steel tubes with drilling holes (openings) (height 120 mm,inner diameter 22 mm), and the stack was subjected to a pressure of2.550 Pa. After calcination, the wafers were cooled under exclusion ofmoisture and packed.

[0067] Product Properties: Thickness: 300 ± 50 μm Vertical dimension:<350 μm (thickness + curvature (bulging)) Moisture content <1% (aftercalcination): Production rejects: <5% Dropping test: <1%

EXAMPLE 11

[0068] 110.5 kg zeolite 4A (water content 20%), 76.0 kg bentonite (watercontent 12%) and 1.9 kg calcium stearate were slurried in a high-shearstirring device (Ultra-Turrax stirrer) in sufficient water to obtain apumpable slurry. The slurry (suspension) was spray-dried so that apowder with a water content of 15.5% (determined by drying at 160° C.)and a particle size distribution of 4%>150 μm and 8%@<45 μm wasobtained. 0.17 g of this material were compressed to a wafer having adiameter of 20 mm using a pressure of 195 MPa, the partial pressure ofwater vapor in the environment (air) surrounding the compression toolswas set to about 12 mbar. The wafers were calcined under the applicationof pressure for 3 hours at 650° C. Thus, 300 wafers were stacked instainless steel tubes with drilling holes (openings) (height 120 mm,inner diameter 22 mm), and the stack was subjected to a pressure of2.550 Pa. After calcination, the wafers were cooled under exclusion ofmoisture and packed.

[0069] Product Properties: Thickness: 300 ± 50 μm vertical dimension:<350 μm (thickness + curvature (bulging)) Moisture content <1% (aftercalcination): Production rejects: <5% Dropping test: <1%

EXAMPLE 12

[0070] 57 kg zeolite 4A (water content 20%), 42 kg of a 50/50 mixture ofattapulgite and kaolin (water content 12%) and 1 kg calcium stearatewere mixed for 2 minutes in an intensive mixer. Then, water was addeduntil there was a substantial increase of viscosity, and mixing wascontinued for 4 minutes. The mixture was dried to a water content of12%, and subsequently granulated and sieved (150 μm sieve). 0.17 g ofthis material having a particle size <150 μm were pressed to a waferunder a pressure of 200 MPa. The wafers were calcined for 3 hours at650° C., cooled with the exclusion of moisture and packed.

[0071] Product Properties: Thickness: 300 ± 50 μm Moisture content <1%(after calcination): Production rejects: 25% Dropping test: 70% fracture

EXAMPLE 13

[0072] An organic electroluminescent element (1) (square, area 12.9cm2), as shown in FIG. 1, was produced using a wafer (circular, diameter27 μm) of Example 4. After fixing the wafer (2) to the back wall (3) ofthe element, it was adhered to the glass substrate (5) of the element bymeans of an adhesive (4) and it was sealed as far as possible by meansof an adhesive. Then, a microphotograph (enlarged 50 times) of thelight-emitting part (6) (consisting of the anode (7), the light-emittinglayer (8) and the cathode (9) of the element was taken. This photographdoes not show dark (non-luminescent) spots, which indicates an attack oncathode (9).

[0073] The element was exposed to a temperature of 85° C. and a relativehumidity of 85% for 500 hours. Subsequently, a new microphotograph ofthe light-emitting part (6) of element (1) was taken. A comparison ofthe two photographs shows that no dark spots were formed, whichindicates an attack on the cathode (9).

EXAMPLE 14 (Comparison)

[0074] An organic electroluminescent element (1) as in Example 9 wasproduced using BaO. As a cover for the BaO, a water-permeable teflonfoil was used which was attached to the back wall (3) by means of a thindouble-adhesive tape. The amount of BaO was adjusted so that the totalmass of BaO, of the teflon foil and the double-adhesive tape exactlycorresponds to that of the wafer produced in Example 9. Thereafter, asdescribed in Example 9, enlarged photographs of the light-emittingelement before and after a storage at 85° C. and 85% humidity for 500hours were taken. A comparison of the two photographs showed asignificantly recognizable growth of dark spots which indicated anattack on cathode (9).

1. A plate-shaped pressed body with a thickness of less than about 700 μm, comprising an inorganic sorbent and a binder wherein the pressed body is obtainable by the process comprising the steps of compressing a mixture comprised of the inorganic sorbent and the binder at a pressure of at least about 70 MPa, wherein the weight ratio of the sorbent to the binder in the mixture is between about 4:1 and 0.7:1 when measured on a dry weight basis and wherein the water content of the mixture determined at 160° C. is between about 8 and 20 percent, and calcining the resulting compressed mixture at a temperature of at least about 500° C. to form the pressed body, wherein water contained in the calcined pressed body is less than about 2 percent.
 2. The pressed body of claim 1 wherein the mixture further comprises a compression aid.
 3. The pressed body of claim 2 wherein the compression aid comprises a fatty acid salt of a divalent or trivalent metal.
 4. The pressed body of claim 1 wherein the calcining is continued until the pressed body has a constant weight.
 5. The pressed body of claim 1 wherein the calcining is continued until the residual moisture content of the pressed body is less than about 1 percent by weight.
 6. The pressed body of claim 1 wherein the inorganic sorbent comprises a natural or synthetic zeolite.
 7. The pressed body of claim 1 wherein the binder comprises a smectite clay.
 8. The pressed body of claim 7 wherein the smectite clay comprises bentonite.
 9. The pressed body of claim 1 wherein the pressed body has a thickness from about 200 to about 400 μm.
 10. The pressed body of claim 1 wherein the ratio of the sorbent to the binder in the mixture on a dry weight basis is between 1.5 to 1 and 1 to
 1. 11. The pressed body of claim 1 wherein the mixture of sorbent and binder are compressed at a pressure from about 100 to about 1300 MPa.
 12. The pressed body of claim 1 wherein the mixture comprises particles, wherein not more than 15 percent of the particles are greater than about 250 μm in diameter.
 13. The pressed body of claim 1 wherein the mixture comprises particles, wherein not more than 8 percent of the particles are greater than about 200 μm in diameter.
 14. The pressed body of claim 1 wherein the mixture comprises particles, wherein not more than 8 percent of the particles are greater than about 150 μm in diameter.
 15. The pressed body of claim 1 wherein the mixture comprises particles, wherein at least about 50 percent of the particles are greater than 45 μm in diameter.
 16. The pressed body of claim 1 wherein the mixture comprises particles, wherein at least about 60 percent of the particles are greater than 45 μm in diameter.
 17. The pressed body of claim 1 wherein the mixture comprises at least about 50 percent spherical particles.
 18. The pressed body of claim 1 wherein the mixture comprises at least about 80 percent spherical particles.
 19. The pressed body of claim 1 wherein the mixture comprises at least about 98 percent spherical particles.
 20. The pressed body of claim 1 wherein the mixture is spray dried prior to compressing.
 21. The pressed body of claim 1 wherein the compressed mixture is calcined under vacuum.
 22. The pressed body of claim 1 wherein the pressed body is calcined under pressure in a perforated tube.
 23. A process for producing pressed bodies comprising mixing an inorganic sorbent and a binder to form a mixture and pressing said mixture at a pressure of at least about 70 MPa, wherein the weight ratio of the sorbent to the binder is between about 4:1 and about 0.7:1 and the water content of the mixture measured at 150° is between about 8 and 20 percent, and calcining the pressed bodies at temperatures of about 500° C. until the water content is less than about 2 percent to form the pressed bodies.
 24. A process for removing moisture from an electronic device by placing the pressed body of claim 1 within the electronic device. 